Methods for the electrolytic production of erythrose or erythritol

ABSTRACT

Methods for the production of erythrose and/or erythritol are provided herein. Preferably, the methods include the step of electrolytic decarboxylation of a ribonic acid or arabinonic acid reactant to produce erythrose. Optionally, the reactant can be obtained from a suitable hexose sugar, such as allose, altrose, glucose, fructose or mannose. The erythrose product can be hydrogenated to produce erythritol.

RELATED APPLICATION

This application claims the benefit of provisional U.S. provisionalpatent application Ser. No. 60/771,549, filed Feb. 8, 2006 andincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to methods of producing erythrose and/orerithritol.

BACKGROUND

Erythritol, a naturally occurring polyol sweetener, can be used toreplace sugar while preserving the sweet taste. Erythritol is afour-carbon sugar polyol (tetritol), which possesses several propertiessuch as sweetness (about 60-80% of sucrose), tooth friendliness, verylow calorific value (0.2 kcal/g, 5% that of sucrose),non-carcinogenicity and, unlike other polyols, causes little, if any,gastrointestinal discomfort (Harald and Bruxelles (1993) Starch/Starke45:400-405). Further, erythritol possesses desirable processingproperties such as heat-stability, and minimal undesirable reactivitywith amino groups so as to resist browning of when present in an organicsubstance. Erythritol can be used as a sweetener, for example inbeverages. For example, U.S. Pat. Nos. 4,902,525 and 6,066,345, JPA7-274829 and EP 0 759 273 relate to the addition of erythritol tobeverages for purposes of flavor enhancement. A chewing gum made with asweetening agent containing erythritol and a liquid sugar or sugaralcohol is disclosed in U.S. Pat. No. 5,120,550. A method of reducingdental cavities by administering a sugarless chewing gum made witherythritol is disclosed in European Patent Publication No. 0 009 325.Low-caloric sweetening compositions containing mesoerythritol aredisclosed in U.S. Pat. No. 5,080,916 and No. 4,902,525 and JapanesePatent Publications No. 89-225458 and 90-104259. Japanese PatentPublication No. 89-51045 discloses chewing gum made with a meltedmixture of mesoerythritol and sugars or sugar alcohols. A sweeteneremploying the use of spray dried erythritol is disclosed in EuropeanPatent Publication No. 0 497 439. A sweetening composition made up oferythritol, sorbitol and a glucose oligomer is disclosed in EuropeanPatent Publication No. 0 511 761.

Erythritol can be found in lichens, hemp leaves, and mushrooms.Erythritol may also be found in fermented foods such as wine, soyasauce, or saki (Sasaki, T. (1989) Production technology of erythritol.Nippon Nogeikagaku Kaishi 63: 1130-1132). Industrial erythritolproduction is typically carried out by one of two approaches: chemicalsynthesis or fermentative biosynthesis.

Chemical synthesis of erythritol typically includes the addition ofcatalysts such as hydrogen and nickel to the raw material sugars underthe environment of high temperature and high pressure. Decarboxylationreactions can be performed with hydrogen peroxide or hypochlorite, forinstance. A suitable method is the so-called Ruff reaction, utilizing acombination of hydrogen peroxide and ferrous sulphate as a catalyticagent (see e.g. Ruff, Berichte der Deutschen Chemischen Gesellschaft 32(1899) 553-554, and E. Fischer, O. Ruff, Ber. 33 (1900) 2142). Reductioncan be carried out chemically, for instance by catalytic hydrogenation,or enzymatically. For example, calcium D-arabinonate may be in thepresence of aqueous hydrogen peroxide solution. Other processes for themanufacture of D-erythrose include the oxidation of D-glucose in thepresence of lead tetraacetate, known under the name of the Perlin method(Perlin A. S., Methods Carbohydr. Chem., 1962, 1, 64), or the acidhydrolysis of 2,4-O-ethylidene-D-erythrose obtained by the oxidationwith periodate of 4,6-O-ethylidene-D-glucose (Schaffer R., J. Am. Chem.Soc., 81 (1959), 2838; Barker R. and MacDonald D. L., J. A. Chem. Soc.,82 (1960),2301). A few improvements in the conversion of gluconic acidto D-arabinose have subsequently been introduced by R. C. Hockett and C.S. Hudson (J. Amer. Chem. Soc., 56, 1632-1633, (1934) and ibid., 72,4546, (1950)) and by the document U.S. Pat. No. 3,755,294. Arabinoseyields of 60%, starting from gluconic acid, are described therein.Progress has been accomplished by V. Bilik (CZ-232647, (1983)) by usingcupric (Cu(II)) ions as catalysts. Yields of the order of 70% areachieved after a laborious purification. Identical results were recentlyobtained with a mixture of ferric and ferrous ions as catalysts(CZ-279002, (1994)). Finally, under specific conditions, the documentEP-A 0,716,067 reports yields of certain aldoses of 78%. Another processis performed by the chemo-reduction of raw materials such asmeso-tartarate (Kent, P. W., and Wood, K. R. (1964) J. Chem. Soc.2493-2497) or erythrose (Otey, F. H., and Sloan, J. W. (1961) Ind. Eng.Chem. 53:267) to obtain erythritol. None of the known chemical synthesistechniques, such as reduction of meso-tartrate, oxidation/reduction of4,6-O-ethylidene-D-glucose and hydrogenation of starch dialdehydehydrolysates (T. Dola and T. Sasaki, Bio-lndustry, (1988), 5, (9), 32),has been widely used for widespread industrial production. Still otherchemical processes developed for the production of erythritol includethe hydrogenation of tartaric acid to yield mixtures of tetritols,including erythritol (U.S. Pat. No. 5,756,865). Tartaric acid estershave also been reduced to yield erythritol (U.S. Pat. No. 2,571,967).

In addition, erythritol can be produced by a number of microorganisms.For example, the erythritol can be produced by fermenting glucose withspecialized yeast strains has been described 5,902,739. Recovery oferythritol from fermentation broths is described in U.S. Pat. No.6,030,820, U.S. Pat. No. 6,440,712 and U.S. Pat. No. 4,906,569.Microorganisms useful in the production of erythritol include highosmophilic yeasts, e.g., Pichia, Candida, Torulopsis, Trigonopsis,Moniliella, Aureobasidium, and Trichosporon sp. (Onishi, H. (1967) HakkoKyokaish 25:495-506; Hajny et al. (1964) Appl. Microbiol. 12:240-246;Hattor, K., and Suziki, T. (1974) Agric. Biol. Chem. 38:1203-1208;Ishizuka, H., et al. (1989) J. Ferment. Bioeng. 68:310-314.) Productionof erythritol by various yeasts have been reported: Debaryomyces (U.S.Pat. No. 2,986,495), Pichia (U.S. Pat. No. 2,986,495), Candida (U.S.Pat. No. 3,756,917), Moniliella (Antonie van Leeuwenhoek, 37 (1971),107-118), and Aureobasidium (JP-A 61/31,091). Two microorganisms,namely, Moniliella tomentosa var. pollinis CBS461.67 and Aureobasidiumsp. SN-G42 FERM P-8940, are known currently to be employed practicallyto produce erythritol. The former is employed, for example, in methodsfor producing polyols in an industrial scale by means of fermentation ofsaccharides (Japanese Patent Publication No. 6-30591 (30591/1994), ibid.6-30592 (30592/1994), ibid. 6-30593 (30593/1994), ibid. 6-30594(30594/1994)), and in these publications methods for producing a seriesof polyols including erythritol are disclosed. However, the strain ofMoniliella tomentosa var. pollinis employed in such methods has a poorsaccharide resistance and suffers from reduced yield of erythritol at ahigh saccharide concentration. Thus, at the saccharide concentration of25 w/v % the saccharide-based erythritol yield (amount of erythritolproduced relative to the amount of saccharide consumed) is as high as42%, but at the saccharide concentration as high as 35 w/v % thesaccharide-based erythritol yield is 33%, and at 35 w/v % the yield isas markedly low as 27%. Often, studies carried out on fermentationtechniques produce erythritol as a secondary constituent. Possibledisadvantages in the production of erythritol by fermentation includefoaming during fermentation, an undesirably slow rate of fermentation,the amount of the byproducts and poor yield.

One of the major drawbacks of the use of erythritol as a sugar replaceris that it is much more expensive than some of the substances which itreplaces. There is a need for improved, cost-effective processes for themanufacture of erythritol, or D-erythrose (converted to erythritol byhydrogenation of the D-erythrose thus obtained).

SUMMARY

The present disclosure relates to new cost-effective methods ofproducing erythrose or erythritol. In a first embodiment, the methodsinclude the step of electrolytic decarboxylation of an arabinonic orribonic acid, to produce erythrose. The electrolytic decarboxylationstep can be performed using a highly crystalline carbon anode. Thearabinonic or ribonic acid reactant is preferably maintained in asolvent, with about 35-80% of the arabinonic or ribonic acidneutralized, more preferably about 50% neutralized, prior to or duringthe electrolytic decarboxylation step. The solvent is preferably water,although other solvents can also be used. For example, the acid solutioncan be an aqueous solution comprising 50% arabinonic acid and 50%arabinonate salt or 50% ribonic acid and 50% ribonate salt, and thetemperature can be maintained at about 25° C., when the electrolyticdecarboxylation step is started. Preferably, the electrolyticdecarboxylation step is stopped at about 80% conversion of the acidfollowed by recycling of the residual acid. Alternatively, the pH may becontrolled by ion exchange or adding un-neutralized starting acid duringthe electrolytic decarboxylation.

Any suitable arabinonic or ribonic acid capable of producing erythroseas a product of the electrolytic decarboxylation step can be used. In afirst aspect, the reactant can be a ribonic acid, arabinonic acid, or amixture thereof, including meso-, d- or I-stereoisomers thereof. In asecond aspect, the erythrose product can be meso-erythrose, D-erythroseor L-erythrose, or purified stereoisomers thereof. Preferably, thereactant of electrolytic decarbodylation step is meso-, d- orI-arabinonic acid, and the product is the resulting form of meso-, d- orI-erythrose.

In a second embodiment, the arabinonic or ribonic acid reactant isobtained from a suitable hexose sugar starting material by any suitablemethod. Preferably, the starting material is selected from the groupconsisting of: allose, altrose, glucose, fructose and mannose, includingany meso-, d- or I-forms thereof. More preferably, the starting materialis d-glucose, fructose or d-mannose. The starting material can beconverted to an arabinonic or ribonic acid by one or more reactionsteps. Preferably, a suitable C-6 sugar starting material isdecarboxylated at the C-1 position by a suitable reaction. For example,D-arabinonic acid may be prepared by oxidizing D-glucose with oxygen gasin an alkaline water solution, oxidation of D-fructose, oxidizingD-glucose with pyranose-2-oxidase to D-arabino-hexos-2-ulose followed bytreatment with a hydroperoxide, or the oxidation of D-glucose toD-arabino-2-hexulosonic acid (or its salt) followed by decarboxylationwith hydrogen peroxide or its salt. Optionally, the hexose sugarstarting material can be synthesized or obtained from any suitablesource or by any suitable synthesis or purification method(s).

In a third embodiment, an erythrose product of the electrolyticdecarboxylation step can be subsequently hydrogenated by any suitablemethod to provide erythritol. For example, erythrose can be reduced byusing hydrogen and a hydrogenation catalyst to produce erythritol. Thereduction can be performed using any suitable reaction, such as aruthenium or nickel catalyst. In one aspect, a hydrogenation can beperformed at temperatures between 70° C. and 150° C., and at pressuresbetween 0.1 and 10 MPa H₂. Alternatively, electrochemical reduction maybe used.

In one particular embodiment, the disclosure provides a method ofproducing erythrose comprising the step of electrolyticallydecarboxylating an acid selected from the group consisting of a ribonicacid and an arabinonic acid in solution to produce erythrose. The methodmay optionally further comprise the step of hydrogenating the erythroseto produce erythritol. The acid is preferably provided as an aqueousaldonic acid solution comprising the ribonic acid and/or the arabinonicacid. Preferably, the acid is a 5-carbon carboxylic acid placed incontact with a highly graphitic anode to permit electrolyticdecarboxylation of the acid to produce erythrose. The ribonic acidand/or the arabinonic acid in the acid solution is preferably providedin a separate step by decarboxylating a sugar selected from the groupconsisting of: allose, altrose, glucose, fructose and mannose, orderivatives, analogs or salts thereof to produce the acid. Optionally,ribonic acid may be provided by the epimerization of aribonic acid. Forexample, U.S. Pat. No. 4,778,531 to Dobler et al., filed Jun. 30, 1987and incorporated herein by reference, describes methods for theepimerization of D-arabinose to D-ribose. The acid solution ispreferably provided by combining an aldonic acid, such as ribonic orarabinonic acid, with a solvent such as water or a water-misciblesolvent to produce the acid solution. For example, one particularlypreferred method of producing erythritol comprises the steps of: (a)oxidatively decarboxylating a sugar selected from the group consistingof: allose, altrose, glucose, fructose and mannose, to provide an acidcomprising a 5-carbon carboxylic acid, preferably an aldonic acid; (b)combining the carboxylic acid with a solvent to produce an aldonic acidsolution; (c) electrolytically decarboxylating the 5-carbon carboxylicacid in the aldonic acid solution to produce erythrose; and (d)hydrogenating the erythrose to produce erythritol. Preferably, thealdonic acid solution has between about 10% and 100%, more preferablyabout 35% to 85%, most preferably about 50%, of the acid neutralizedprior to the electrolytic decarboxylation. The electrolyticdecarboxylation is preferably performed until up to about 80% of theacid is converted in the presence of a highly graphitic electrodeconfigured as an anode. Residual aldonic acid from the decarboxylationstep may be recycled by contacting unreacted aldonic acid with an ionexchange material or adding non-neutralized acid, followed by repeatingthe oxidative decarboxylation step to produce erythrose.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a reaction scheme showing various reaction steps usingcertain allose, altrose, glucose or mannose starting materials.

FIG. 1B is a reaction scheme using certain glucose or fructose startingmaterials.

FIG. 2 is a reaction scheme showing examples of certain preferredreaction steps.

FIG. 3 is a schematic of an electrolytic oxidative decarboxylation stepfor the production of erythrose.

DETAILED DESCRIPTION

The methods for the production of erythrose and/or erythritol disclosedin the present disclosure preferably include the step of thedecarboxylation of an arabinonic or ribonic acid substrate. Thedecarboxylation step can be an oxidative decarboxylation performed by anelectrolytic decarboxylation of an arabinonic or ribonic acid reactantto produce an erythrose product. Preferably, the erythrose ishydrogenated to produce erythritol.

Definitions

As used herein, the term “aldonic acid” refers to any polyhydroxy acidcompound comprising the general formula HOCH₂[CH(OH)]_(n)C(═O)OH (wheren is any integer, including 1-20, but preferably 1-12, more preferably5-8), as well as derivatives, analogs and salts thereof. Aldonic acidscan be derived, for example, from an aldose by oxidation of the aldehydefunction (e.g., D-gluconic acid).

Recitation of “erythrose” herein refers to an aldose (tetrose)carbohydrate with chemical formula C₄H₈O₄, including any stereoisomers,derivatives, analogs and salts thereof. Unless otherwise indicated,recitation of “erythrose” herein is intended to include, withoutlimitation, the molecules: D-(−)-Erythrose, L(+)-Erythrose,D(−)-Erythrose, D-Erythrose, L-Erythrose and D(−)-Erythrose andmeso-erythrose. A Fischer Projection of the D-erythrose structure (1) isprovided below.

The term “erythritol” herein, unless otherwise specified, includesmolecules with the chemical formula C₄H₁₀O₄, as well as anystereoisomers, derivatives and analogs thereof. Unless otherwiseindicated, recitation of “erythrose” herein is intended to include,without limitation, the molecules: D-(−)- meso-erythritol,(D)-Erythritol, (L)-Erythritol,(R*,S*)-1,2,3,4-butanetetrol;(R*,S*)-tetrahydroxybutane; erythrol;erythrite; 1,2,3,4-butanetetrol, (R*,S*)—; erythritol, and phycitol. AFischer Projection of the D-erythritol structure (2) is provided below.

The term “decarboxylation” as used herein refers to the removal of acarboxyl group (—COOH) by a chemical reaction or physical process.Typical products of a decarboxylation reaction may include carbondioxide (CO₂) or formic acid.

The term “electrochemical” refers to chemical reactions that can takeplace at the interface of an electrical conductor (an electrode) and anionic conductor (the electrolyte). Electrochemical reactions can createa voltage potential between two conducting materials (or two portions ofa single conducting material), or can be caused by application ofexternal voltage. In general, electrochemistry deals with situationswhere an oxidation and a reduction reaction is separated in space. Theterm “electrolytic” as used herein refers to an electrochemicaloxidation or reduction reaction that results in the breaking of one ormore chemical bonds. Electrolytic reactions as used herein preferablydescribe reactions occurring as a product of interaction with a cathodeor anode.

As used herein, “derivative” refers to a chemically or biologicallymodified version of a chemical compound that is structurally similar toa parent compound and (actually or theoretically) derivable from thatparent compound. A derivative may or may not have different chemical orphysical properties of the parent compound. For example, the derivativemay be more hydrophilic or it may have altered reactivity as compared tothe parent compound. Derivatization (i.e., modification) may involvesubstitution of one or more moieties within the molecule (e.g., a changein functional group) that do not substantially alter the function of themolecule for a desired purpose. The term “derivative” is also used todescribe all solvates, for example hydrates or adducts (e.g., adductswith alcohols), active metabolites, and salts of the parent compound.The type of salt that may be prepared depends on the nature of themoieties within the compound. For example, acidic groups, for examplecarboxylic acid groups, can form, for example, alkali metal salts oralkaline earth metal salts (e.g., sodium salts, potassium salts,magnesium salts and calcium salts, and also salts quaternary ammoniumions and acid addition salts with ammonia and physiologically tolerableorganic amines such as, for example, triethylamine, ethanolamine ortris-(2-hydroxyethyl)amine). Basic groups can form acid addition salts,for example with inorganic acids such as hydrochloric acid, sulfuricacid or phosphoric acid, or with organic carboxylic acids and sulfonicacids such as acetic acid, citric acid, benzoic acid, maleic acid,fumaric acid, tartaric acid, methanesulfonic acid or p-toluenesulfonicacid. Compounds which simultaneously contain a basic group and an acidicgroup, for example a carboxyl group in addition to basic nitrogen atoms,can be present as zwitterions. Salts can be obtained by customarymethods known to those skilled in the art, for example by combining acompound with an inorganic or organic acid or base in a solvent ordiluent, or from other salts by cation exchange or anion exchange.

As used herein, “analogue” refers to a chemical compound that isstructurally similar to another but differs slightly in composition (asin the replacement of one atom by an atom of a different element or inthe presence of a particular functional group), but may or may not bederivable from the parent compound. A “derivative” differs from an“analogue” in that a parent compound may be the starting material togenerate a “derivative,” whereas the parent compound may not necessarilybe used as the starting material to generate an “analogue.”

Any concentration ranges, percentage range, or ratio range recitedherein are to be understood to include concentrations, percentages orratios of any integer within that range and fractions thereof, such asone tenth and one hundredth of an integer, unless otherwise indicated.Also, any number range recited herein relating to any physical feature,such as polymer subunits, size or thickness, are to be understood toinclude any integer within the recited range, unless otherwiseindicated. It should be understood that the terms “a” and “an” as usedabove and elsewhere herein refer to “one or more” of the enumeratedcomponents. For example, “a” polymer refers to one polymer or a mixturecomprising two or more polymers. As used herein, the term “about” refersto differences that are insubstantial for the relevant purpose orfunction.

Electrochemical Decarboxylation

The step of oxidative decarboxylation of a reactant substrate ispreferably performed by an electrochemical oxidative decarboxylation ofthe reactant substrate. FIG. 1A shows a schematic diagram describingvarious methods related to the production of erythrose and erythritol.Preferably, the methods include the step of electrolytic decarboxylationof a suitable reactant to produce erythrose. The reactant can beprovided as a solution of the reactant placed in contact with anelectrode to effect a decarboxylation of the reactant so as to producean erythrose.

According to a first embodiment, any suitable arabinonic or ribonic acidcapable of producing erythrose as a product of an electrolyticdecarboxylation step can be used as a reactant. The reactant ispreferably a 5-carbon carboxylic acid, such as a ribonic acid or anarabinonic acid, including one or more stereoisomers (e.g., D-, L-, ormeso-forms) or enantiomers of the reactant products, as well as suitablederivatives, analogs and salts of the reactants. Suitable reactantsinclude derivatives and analogs of the carboxylic acid reactant caninclude reactants with chemical structure variations thatinsubstantially vary the reactivity of the molecule from undergoing anelectrolytic decarboxylation process to produce either erythrose or anintermediate that can be converted to erythrose. For example, referenceto an “arabinonic acid” reactant includes D-arabinonic acid,L-arabinonic acid and meso-arabinonic acid. In certain preferred aspectsof the first embodiment, the reactant can be a ribonic acid, arabinonicacid, or a mixture thereof, including meso-, d- or I-stereoisomersthereof; the erythrose product can be meso-erythrose, D-erythrose orL-erythrose, or purified stereoisomers thereof. Preferably, the reactantof electrolytic decarboxylation step is meso-, d- or I-arabinonic acid,and the product is the resulting form of meso-, d- or I-erythrose.

FIG. 1A shows a first aspect of the first embodiment, whereby aD-ribonic acid is a first reactant 40 that undergoes a decarboxylationreaction 50 to produce a D-erythrose product 110. Also shown is analternative aspect of the first embodiment, wherein a D-arabinonic acidis a second reactant 90 that undergoes an oxidative decarboxylationreaction 100 to produce the D-erythrose product 110. Optionally, thefirst reactant 40 can be obtained by a first conversion reaction 140 ofD-arabinonic acid to D-ribonic acid. Alternatively, the second reactant90 can be obtained by a second conversion reaction 150 of D-ribonic acidto D-arabinonic acid. While the decarboxylation reactions 50, 100 arepreferably decarboxylation reactions that produce an aldehyde product,although other reaction products such as carboxylic acids can also beproduced and preferably partially reduced to provide the aldehydeproduct 110, such as D-erythrose.

Preferably, the decarboxylation reaction 50, 100 is performedelectrochemically. In one aspect, electrolytic decarboxylation of areactant in a solution provides a desired product or intermediate thatcan be subsequently converted to the desired product. Preferably, thereactant is a ribonic acid, such as D-ribonic acid, or an arabinonicacid, such as D-arabinonic acid, and the product is an erythrose, suchas D-erythrose. The reactant can be provided in a suitable solutioncomprising at least the reactant and a solvent. The reactant can bedissolved in the solvent by any suitable method, including stirringand/or heating where appropriate. The solvent can be any solvent inwhich the reactant can dissolve to a desired extent. Preferably, thesolvent is water, any water-miscible solvent such as an alcohol, or acombination thereof. For example, solvents can comprise one or more ofthe following: water, methanol, ethanol, propanol, dioxane andacetonitrile. The solution is preferably an acidic solution comprising aribonic acid or arabinonic acid, or a combination thereof.

Preferably, at least about 10% of the acid is neutralized or exists as acorresponding salt thereof. For example, the acid reactant solution canbe provided with about 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100% ofone or more reactant acids neutralized. Preferably, 10%-100% of at leastone ribonic acid or arabinonic acid reactant is neutralized. Morepreferably, about 35%-80% of a ribonic acid or arabinonic acid reactantpresent is neutralized. Most preferably, about 50% of the ribonic acidor arabinonic acid reactant present in a reactant acid solution isneutralized.

In one aspect, the reactant acid solution is provided at about 10-100%neutralization, more preferably about 35-80% neutralization and mostpreferably about 50% neutralization of the reactant acid. The pH can bepermitted to increase as the electrolytic reaction proceeds. Optionally,the pH could be provided and/or maintained within a desirable rangethroughout the reaction, for example by conducting the reaction incontact with an ion exchange resin. The pH could also be controlled bythe addition of non-neutralized starting acid. The pH could also becontrolled by using a divided electrolytic cell with a cation exchangemembrane. The reactant acid solution can have any suitable pH to providea desired concentration of dissociated reactant. For a reactant acidsolution comprising an ribonic acid, the pH is preferably between about3.0 and 4.0 prior to beginning the decarboxylation reaction. For areactant solution comprising an arabinonic acid reactant, the pH ispreferably between 3.0 and 4.0 prior to beginning the decarboxylationreaction.

Optionally, the residual reactant can be recycled by separating thestarting material from products, for example by use of an anionicexchange resin. A partially decarboxylated solution of acid can containboth the starting acid (e.g., arabinonic acid) and the aldehydic product(e.g., erythrose). The negatively charged arabinonic acid can adhere topositively charged anionic exchange media. A partially reacted solutioncan be passed over a bed or column of ion exchange resin beads toreplace the arabonate with OH—. The solution can then be passed overcationic resin to strip any cations and neutralize the OH—. Theresulting solution can comprise higher levels of the nonionic species(e.g., erythrose). Once the anionic exchange resin is saturated witharabinonate, it can be removed by treating the resin with OH—. While theion exchange resin recycling process has been illustrated with respectto hydroxyl (OH—) functional groups, other suitable groups may also beemployed.

Electrolytic Apparatus

The electrochemical decarboxylation of a suitable acid reactant can beperformed using any suitable structure. Preferably, the electrochemicaldecarboxylation is performed by contacting an acid reactant solutioncomprising a ribonic acid or an arabinonic acid with an anode, where thereactant can be oxidized and decarboxylated. Contact between thestarting material and the anode can elicit the decarboxylation, whichcan result in liberation of carbon dioxide and formation of a productsuch as erythrose. The product of the decarboxylation is preferably analdehyde such as erythrose, or an intermediate such as an analog orderivative of erythrose that can be converted to erythrose or othersuitable aldehyde.

Preferably, the electrochemical decarboxylation of the reactant isconducted in an apparatus having any configuration comprising an anodein electrically conducting communication with a cathode. FIG. 3 shows aschematic of an electrochemical apparatus for decarboxylation of areactant acid to form a desired product, such as erythrose. Theapparatus comprises an anode 502 connected through a means forelectrical conduction 504 to a cathode 508.

The anode 502 preferably comprises a carbon reactive surface whereoxidation of the reactant acid can occur. The electrochemical cell anodecan be formed from any suitable material such as graphite, pyrolyticcarbon, wax-impregnated graphite, glassy carbon, dispersed graphite,dispersed carbonaceous material, carbon cloth, coke, or platinum as aplaner, packed bed, fluidized bed, or porous anode. Most preferably, theanode reactant surface comprises a highly crystalline graphiticmaterial, such as a graphite foil. Other, less preferred, materials suchas platinum or gold can also be used to form the reactive surface of theanode. The reactant acid 310 can be a ribonic acid or arabinonic acidthat is oxidized at or near the reactant surface of the anode 502 toform a product 320 such as erythrose. The anode surface area ispreferably large and is preferably made of a carbonaceous material,platinum, or other metal.

Preferably, the electrochemical cell further comprises a cathode 508,where a reduction can occur within the electrochemical cell. The cathode508 can be formed from any suitable material having a desired level ofelectrical conductivity, such as stainless steel. In one aspect, thedecarboxylation reaction at the anode can be:

arabinate-2e⁻→erythrose+CO₂+water

The counter electrode reaction can be:

2H₂O+2e⁻→2OH⁻+H₂

Typically, some current can be lost to the production of O₂ gas at theanode.

The electrochemical apparatus can be configured to permit ions 400 suchas cations (for example, protons) generated by the oxidativedecarboxylation to be transported to the vicinity of the cathode 508.The electrochemical apparatus can comprise a means for transporting ions506 such as cations (such as protons) between a first solution orsolution portion contacting the anode into a second solution or solutionportion contacting the cathode. The first solution and second solutionare optionally sequestered in separate cells that can be separated bythe means for transporting ions.

The electrolytic cell can have any suitable configuration. An apparatusfor the decarboxylation of a reactant substrate preferably comprises anelectrochemical cell. The electrochemical cell can be configured tomaintain the acid solution comprising the reactants in contact with ananode (undivided configuration). Optionally, a cathode can be maintainedin contact with the acid solution in the same cell as the anode, or in aseparate, second half-cell (a divided configuration). In the dividedconfiguration, a means for ion transport preferably connects the firstand second cell, such as a semi-permeable membrane. Preferably, themembrane is permeable to protons. Other suitable configurations for theelectrolytic cell include a flow-through reactor configuration, a packedbed configuration, a batch cell configuration or a fluidized bedconfiguration.

U.S. Pat. No. 4,950,366, which is incorporated by reference in itsentirety, discloses one example of a suitable apparatus for thedecarboxylation of D-gluconic acid to yield D-arabinose that can be usedto perform the oxidative decarboxylation reaction. The electrochemicalcell preferably comprises an electrochemical cell anode, where theoxidative decarboxylation reaction is believed to occur.

The methods for producing erythrose using an electrolytic apparatus canyield about 20, 30, 40, 40, 50, 60, 70, 80, 85, 90, 95 or up to 100% ofthe theoretical yield, preferably at least about 35%, more preferably atleast about 60%, even more preferably at least about 80%, or mostpreferably at least about 95% or more of theoretical yield.

Hexose Starting Materials

In a second embodiment, the arabinonic or ribonic acid reactant can beobtained from a suitable hexose starting material by any suitablemethod. Referring again to FIG. 1A, preferred starting materials areselected from the group consisting of: allose 10, altrose 20, glucose 60and mannose 70. While the D-stereoisomer of the starting materials areshown in the embodiments illustrated in FIG. 1, any suitablestereoisomer may be used, including the D-, L- or meso- forms of theillustrated starting materials. Alternatively, D-ribonic acid can beused as a starting material 40 to produce D-arabinonic acid reactant 90by process 150, or vice versa (by process 140). Preferably, the startingmaterial is a meso-, d- or I- form of glucose, fructose or mannose,although any suitable derivative or analog of the allose 10, altrose 20,glucose 60 or mannose 70 materials can be used as a starting materialthat permits conversion of the starting material to a desired reactantcan be used. Fructose is also a preferred starting material. Referringto FIG. 1B, another preferred reaction scheme 200 shows the conversionof a starting material comprising fructose 210, glucose 220, or amixture of fructose 210 and glucose 220, to arabinonic acid 290 by anoxidative decarboxylation reaction 280. The arabinonic acid 290 ispreferably D-arabinonic acid 90, suitable as a reactant in theelectrolytic decarboxylation reaction 100 described above with respectto FIG. 1A.

The oxidative decarboxylation reactions 30, 80, 280 can be performed ona reactant substrate using various chemical reactions. Examples ofsuitable chemical oxidative decarboxylation approaches include, but notlimited to, the use of a transition metal ion catalyst with a primaryoxidizing agent or the use of a hypochlorite/hypochlorous acid. Inanother aspect, a chemical oxidative decarboxylation is performed usingtransition metal ion catalyst such as: Fe(III) or Cu(II) with a primaryoxidizing agent such as hydrogen peroxide to regenerate the catalyst.The chemical oxidative decarboxylation can be performed using a coppertransition metal ion catalyst, such as a Cu(II) catalyst, in combinationwith any suitable primary oxidizing agent. For example, a Ruffdegradation procedure can be performed, preferably using copper ionsrather than iron for the Ruff degradation of acidic sugars (CS Patent232647 and FR Patent 2771413). The Ruff degradation is described in W.Pigman et al., “The Carbohydrates,” Academic Press, New York, 2nd Ed.,Vol. IA (1972), Vol. IB (1980), portions of which relevant to oxidativedecarboxylations of carbohydrates are incorporated herein by reference.

Referring again to FIG. 1B, the D-arabinonic acid 290 is preferablyprepared by oxidizing a starting material comprising glucose 220 orfructose 210 with oxygen gas in an alkaline water solution (for example,as described in U.S. Pat. No. 4,125,559 and U.S. Pat. No. 5,831,078,incorporated herein by reference). Preferably, the starting materialcomprising glucose 220, fructose 210, or a mixture thereof, is reactedwith an alkali metal compound in aqueous solution by first heating thealkali metal compound in aqueous solution at a temperature between about30° C. and 100° C., then passing oxygen into the solution at a pressureof between about 1.5 to about 40 bar, and finally adding the startingmaterial and permitting the reaction to continue for at least about 4.5hours per mole of starting material while stirring the reaction mixture.Alternatively, the starting material can be heated initially in theaqueous solution instead of the alkali metal compound, and the alkalimetal compound can be added to the reaction mixture in the last step,instead of the starting material and after the oxygen is added. Thestarting material is preferably a D-Hexose such as D-glucose, D-fructoseor D-mannose, which can be present in various ring forms (pyranoses andfuranoses) and as various diastereomers, such as α-D-glucopyranose andβ-D-glucopyranose. The starting material can be reacted with the alkalimetal compound in a stoichiometric amount, or in excess, preferablyusing an amount of from 2 to 5 equivalents of the alkali metal compoundper mole of the D-hexose starting material. Preferred alkali metalcompounds are hydroxides, oxides and alcholates, especially sodium orpotassium compounds. Examples of suitable alkali metal compounds includepotassium hydroxide, sodium hydroxide, sodium ethylene glycolate, sodiummethylate, sodium propylate, sodium ethylate, sodium tripropyleneglycolate and potassium tert-butylate. The oxygen is preferably used asa mixture with inert gas, such as in the form of air, with O₂ in astoichoimetric amount or in excess, but preferably with an amount offrom 1 to 20 moles of O₂ per. mole of the D-hexose starting material.

The reaction is preferably carried out at above 30° C., but preferablybetween about 40 to 60° C., and under a pressure of about 1.5 to 40bars, preferably between 18 to 25 bars. The reaction may be performedcontinuously or batchwise, in a suitable solvent. The solvent ispreferably water, desirably in an amount that is about 2 to 100 times,preferably from about 2 to 30 times, the weight of D-hexose startingmaterial added. The water may be added separately, or preferablytogether with, the alkali metal compound or the hexose startingmaterial, most preferably in the form of an aqueous solution of thealkali metal compound or aqueous solution of the hexose startingmaterial. Preferably, aqueous solutions with the alkali metal compoundcontain about 1 to 50 weight percent of the alkali metal compound or thehexose starting material. The total reaction time is preferably betweenabout 4.5 and 9.0 hours per mole of the hexose starting material. Thereaction mixture is preferably thoroughly stirred during the entirereaction, for example by stirring at speeds of about 1,200 to about2,000 rpm. Mixing of the reaction mixture is preferably begun afteraddition of the hexose starting material. Alternatively, fructose 210(preferably, D-fructose) can be converted to D-arabinonic acid byreaction with oxygen gas in an alkaline water solution as described inJ. Dubourg and P. Naffa, “Oxydation des hexoses reducteur par I'oxygeneen milieu alcalin,” Memoires Presentes a la Societe Chimique, p. 1353,incorporated herein by reference.

In another aspect of the second embodiment, D-arabinonic acid reactant90 may be prepared by decarboxylation 80 of a D-glucose startingmaterial 60 by one or more reactions. Referring to FIG. 2, the startingmaterial can be converted to an arabinonic reactant 90 or a ribonic acidreactant 40 by one or more reaction steps. Preferably, a suitable C-6sugar starting material is decarboxylated at the C-1 position.Optionally, a starting material comprising D-(+)-allose or D-(+)-altrosecan undergo a decarboxylation reaction 35 to produce an intermediatecomprising D-(−)-ribose (aldehyde) that can subsequently undergo anoxidation reaction 37 to produce the desired reactant 40 comprisingD-ribonic acid. Similarly, a starting material comprising D-(+)-glucoseor D-(+)-mannose can undergo a decarboxylation reaction 85 to produce anintermediate comprising D-(−)-arabinose (aldehyde) that can subsequentlyundergo an oxidation reaction 87 to produce the desired reactant 90comprising D-arabinonic acid. U.S. Pat. No. 4,515,667 describes aprocess for the photochemical decarboxylation of an alpha-hydroxycarboxylic acid to the corresponding alcohol which process comprisesirradiating a mixture of a solution of an alpha-hydroxy carboxylic acidand a metal titanate.

D-arabinonic acid can also be produced from D-glucose by oxidation ofD-glucose with pyranose-2-oxidase to D-arabino-hexos-2-ulose (U.S. Pat.No. 4,423,149) and treating this with hydrogen peroxide (Carbohydr. Res.127 (1984) 319) or other hydroperoxides. The reaction ofD-arabino-hexos-2-ulose and hydrogen peroxide is fastest and mostselective in alkaline solutions while the products comprise the salts ofD-arabinonic and formic acids. Under acidic conditions e.g. performicacid (i.e. a mixture of formic acid and hydrogen peroxide) may beapplied as the oxidant. 0.3M D-erythro-pentos-2- ulose can be oxidizedwith 0.6M performic acid. The reaction is complete in 10 minutes andresults in the formation of D-erythrono-1,4-lactone, 3- and4-o-formyl-D-erythronic acids and the unsubstituted D-erythronic acid.The o-formyl groups are rapidly hydrolyzed in an aqueous solution. Stillanother way of producing D-arabinonic acid is to oxidize D-glucose toD-arabino-2-hexulosonic acid (or its salt) and decarboxylate it withhydrogen peroxide or its salt (JP 15,610 (′63), Carbohydr. Res. 36(1974) 283-291). D-arabino-2-Hexulosonic acid can be produced throughfermentation (U.S. Pat. Nos. 3,255,093 and 3,282,795), catalyticoxidation (EP-A-O-, 1 51,498) or a two-step enzymatic oxidation (U.S.Pat. No. 4,423,149). The advantage of the route viaD-arabino-2-hexulosonic acid is that formic acid is not generated, whichenables a more direct hydrogenation of the de-ionized oxidation productmixture with the ruthenium catalyst.

Analogous or similar reactions can be performed on other startingmaterials to generate suitable reactant materials. In a second aspect ofthe second embodiment, D-arabinonic acid reactant 90 may be prepared bydecarboxylation 80 of a D-mannose starting material 70 by one or morereactions. In a third aspect of the second embodiment, D-ribonic acidreactant 40 may be prepared by decarboxylation 30 of a D-allose startingmaterial 10 by one or more reactions. In a fourth aspect of the secondembodiment, D-ribonic acid reactant 40 may be prepared bydecarboxylation 30 of a D-altrose starting material 20 by one or morereactions. Still other starting materials can also be used. For example,D-arabinonic acid is also formed as the main product in a similaroxidation of D-fructose (Carbohydr. Res. 141 (1985) 319). The startingmaterials can also be converted to aldonic acids and subsequentlyreacted to form a suitable reactant such as the arabinonic acid orribonic acid. One suitable chemical oxidative decarboxylation isperformed using hypochlorite/hypochlorous acid. Amides of sugar acidscan also be decarboxylated from hypochloride (Hoffman degradation). TheHoffman degradation can also be used for the decarboxylation of aldonicacid starting materials. Further details on the oxidativedecarboxylation of carbohydrates using hypochlorite/hypochlorous acidare found in R. L. Whistler et al, “Preparation of D-arabinose andD-glucose with hypochlorite,” Journal of the American Chemical Society,81, 46397 (1981), which is incorporated herein by reference. Suitablestarting materials such as a hexose starting material can be synthesizedor obtained from any suitable source or by any suitable synthesis orpurification method(s).

Conversion of Erythrose to Ervthritol

In a third embodiment, an erythrose product of the electrolyticdecarboxylation step can be converted to erythritol by any suitablemethod, during or after the oxidative decarboxylation. The conversion oferythrose to erythritol can be performed using any suitable reduction orhydrogenation reaction.

Preferably, erythrose can be reduced by using hydrogen and ahydrogenation catalyst to produce erythritol. The reduction can beperformed using any suitable reaction, such as a ruthenium or nickelcatalyst. In one aspect, a hydrogenation can be performed attemperatures between 70° C. and 150° C. and at pressures between 0.1 and10 MPa H₂. For example, U.S. Pat. No. 6,300,049 describes certainmethods for the manufacture of erythritol by hydrogenation ofD-erythrose wherein from 1 to 10% by weight of catalyst is used withrespect to the sugar, as dry matter, and subjected to the hydrogenation.In this reaction, the hydrogenation is preferably carried out on syrupswith a dry matter content of between 15 and 50%, preferably 30 to 45%,under a hydrogen pressure of between 20 and 200 bars. Hydrogenation canbe carried out continuously or batchwise. When batchwise hydrogenationis carried out, the hydrogen pressure used is generally between 30 and60 bars and the temperature at which the hydrogenation is carried out isbetween 100 and 150° C. The pH of the hydrogenation mixture can bemaintained by the addition of sodium hydroxide or of sodium carbonate,for example, preferably without exceeding a pH of 9.0. Preferably, thehydrogenation minimize the production of cracking or isomerizationproducts. Hydrogenation reaction is preferably halted when the contentof reducing sugars in the reaction mixture has become less than 1%, morepreferably less than 0.5% and more particularly less than 0.1%. Aftercooling the reaction mixture, the catalyst is removed by filtration andthe D-erythritol thus obtained is demineralized through cationic andanionic resins. At this stage, the syrup preferably contains at least90% of D-erythritol, which is readily purified by crystallization afterconcentrating and cooling the solutions. One example of a suitableruthenium catalyst (20% catalyst on total dry substance) is supported onactive carbon (5% Ru on carbon).

Alternatively, erythrose is converted to erythritol by electrochemicalhydrogenation of erythrose. For example, the erythrose can behydrogenated at an electrode, preferably a cathode, formed from asupport material adhered to a suitable conductive material. Theelectrode may have any suitable configuration, including perforatedmaterials such as nets, metal meshes, lamellae, shaped webs, grids andsmooth metal sheets. In one aspect, the cathode can be a plane-parallelelectrode configured as a planar sheet, or a candle-type electrodesconfigured as a cylinder. In one embodiment, the electrode is preferablya cathode comprising a conducting material adhered to a porous support.The electrode can have any suitable shape and configuration including aplanar sheet or tube configured as a plurality of particles impregnatedin a mesh support or an aggregated layer of particles adhered to thesurface of a cylindrical planar support sheet.

U.S. Pat. No. 5,919,349, filed May. 20, 1997 by Huber et al., which isincorporated herein by reference, describes one suitable electrodestructure comprising a layer of conductive particles adhered to a poroussupport. The support is preferably configured as a porous conductivematerial such as steel, nickel, nickel alloys, tantalum, platinizedtantalum, titanium, platinized titanium, graphite, electrode carbon andsimilar materials, alloys and mixtures thereof. An electricallyconductive material may be attached to the support material, preferablyin a particulate form. The conductive material preferably forms acathodically polarized layer when deposited on the support material.Preferably, the conductive material is formed from metal particles,conductive metal oxides or a carbonaceous material. Suitable metals forthe conductive layer include Group I, II and VIII metals from thePeriodic Table, especially Co, Ni, Fe, Ru, Rh, Re, Pd, Pt, Os, Ir, Ag,Cu, Zn, Pb and Cd, of which Ni, Co, Ag and Fe are preferably used asRaney Ni, Raney Co, Raney Ag and Raney Fe. The conductive material maybe doped with small amounts of metals such as Mo, Cr, Au, Mn, Hg, Sn orother elements of the Periodic Table of the Elements, especially S, Se,Te, Ge, Ga, P, Pb, As, Bi and Sb. The conductive material may also be ametal oxide such as magnetite or a carbonaceous material such asgraphite, activated carbon or carbon black.

Particularly preferred conductive materials are particles of: Pd/C,Pt/C, Ag/C, Ru/C, Re/C, Rh/C, Ir/C, Os/C and Cu/C, optionally doped withmetals or other elements of the Periodic Table of the Elements,including S, Se, Te, Ge, Ga, P, Pb, As, Bi and Sb. The conductive metalmaterials may be adhered to the support by any suitable method, such asreducing salts of metals in contact with the support, such as metalhalides, metal phosphates, metal sulfates, metal chlorides, metalcarbonates, metal nitrates and the metal salts of organic acids,preferably formates, acetates, propionates and benzoates, especiallypreferably acetates. The pore size of the support is generally about 1to 500 μm, preferably about 5 to 300 μm and most preferably about 50 to200 μm, and the porous support material preferably has a void-to-volumeratio of at least about 0.2, and preferably up to about 0.7 (i.e., up to70% porous). The pore size of the support generally exceeds the meandiameter of the particles forming a layer of conductive materialdeposited on the support. Preferably the pore size of the support isabout twice to four times as large as the mean particle size of theparticles forming the layer. Alternatively, supports may have other poresizes which are smaller than the mean particle size of the particlesforming the layer.

Alternatively, a hydride reducing agent may also be used to converterythrose to erythritol. For example, erythrose produced from theelectrolytic decarboxylation reaction can be converted to erythritol byadding an excess of sodium borohydrate to a solution comprising theerythrose. Examples of hydride reducing agents are sodium borohydride,lithium borohydride, lithium aluminum hydride, with potassiumborohydride (KBH₄) or sodium borohydride being the preferred reducingagent (NaBH₄).

A reduction can also be a hydrogenation reaction performed with hydrogenand a ruthenium (See WO Patent Appl. No. 2004/052813, incorporatedherein by reference), nickel (U.S. Pat. No. 4,008,285, incorporatedherein by reference), or other hydrogenation catalysts according toknown art to produce polyols from aldoses. Alternatively,electrochemical reduction may be used (Taylor, Chemical andMetallurgical Engineering, Vol. 44 (1937) 588, which is incorporatedherein by reference). Still other methods useful for the electrolytichydrogenation of erythrose to erythritol are described in the followingreferences: V. Anantharaman et al., “The Electrocatalytic Hydrogenationof Glucose II. Raney Nickel Powder Flow-Through Reactor Model,” J.Electrochem. Soc., vol. 141, No. 10, Oct. 1994, pp. 2742-2752; and Cocheet al., “Electrocatalytic Hydrogenation Using Precious MetalMicroparticles in Redox-Active Polymer Films”, J. Org. Chem., vol. 55,No. 23, pp. 5905-5910 (1990).

EXAMPLES

The following examples are to be considered illustrative of variousaspects of the invention and should not be construed to limit the scopeof the invention, which are defined by the appended claims.

Experimental Procedure:

The experiments detailed in Examples 1-2 were performed in a glass cellusing a graphite foil flag anode. The glass cell consisted of a largetest tube, a 5 cm² stainless steel cathode flag welded to a titaniumrod, and a 5 cm² Grafoil flag (AET GrafTech, 0.03″ thick) attached to agraphite rod current collector.

Example 1 Electrolytic Decarboxylation of Ribonic Acid

Sodium ribonate (15 mmoles) was dissolved in 20 mL of water. Cationexchange resin (Amberlite IRC747 H+ form) was added to lower the pH from6.8 to 3.5 (or approximately 50% neutralization of the startingmaterial). The solution was filtered to remove the cation resin, theribonate starting material was diluted to 30 mL, and 25 mL transferredto glass cell for electrolysis. The initial ribonate solution wasanalyzed by HPLC against a standard and quantified to be 9.54 mmoles(0.38M). The 25 mL of starting material containing 9.54 mmoles ofribonate was stirred in the glass cell, while a constant current of 0.5amps (100 mA/cm²) was applied. The cell voltage averaged about 6.5volts, and the pH of the substrate increased from 3.5 to 7.6 after 2F/mole of charge was passed. Samples were taken at 603, 1206 and 1809coulombs. The samples containing the erythrose product were reduced toerythritol with an excess amount of sodium borohydride, and analyzed forerythritol by HPLC-RI. The samples were quantified for erythritol basedon a response factor determined from an erythritol standard, see Table1.

TABLE 1 Erythritol Charge Conc. Erythritol Sample # F/mole mg/mL Yield,% 652-25A 0 0 — 652-25B 0.7 12.8 27.4 652-25C 1.3 28.7 61.7 652-25D 2.037.8 81.1

Example 2 Electrolytic Decarboxylation of Arabinonic Acid

Potassium arabonate (15 mmoles) was dissolved in 20 ml of water. Thearabonate was acidified to approximately 50% neutralization by addingcation exchange resin (Amberlite IRC747 H+form) and lowering the pH from8.4 to 3.5. The arabonate was filtered to remove the resin, diluted to30 mL, and transferred to a glass cell for electrolysis. The initialarabonate was quantified by HPLC-RI against an arabonate standard andwas found to contain 9.2 mmoles (0.37M). There was a loss of 3.3 mmolesof arabonate from the cation exchange resin.

The 25 mL of starting material containing 9.2 mmoles of arabonate wasstirred in the glass cell, while a constant current of 0.5 amps (100mA/cm²) was applied. The cell voltage averaged about 5.5 volts, and thepH of the substrate increased from 3.5 to 7.7 after 2 F of charge waspassed per mole of starting material. Samples were taken at 603, 1206and 1809 coulombs. The samples containing erythrose were reduced toerythritol with an excess amount of sodium borohydride, and analyzed forerythritol by HPLC-RI. The samples were quantified for erythritol basedon a response factor determined from a known standard, see Table 2.

TABLE 2 Erythritol Charge Conc. Erythritol Sample # F/mole mg/mL Yield,% 652-29A 0 0 — 652-29B 0.68 8.1 12.9 652-29C 1.4 24.1 53.3 652-29D 2.027.3 60.4

Theoretical Example 1 Oxidative Decarboxylation of Glucose StartingMaterial to Form Arabinonate

One suitable example of a reaction for the oxidative decarboxylation ofa glucose starting material to arabinonate is provided in U.S. Pat. No.4,125,559 to Scholz et al., filed May. 19, 1977 and issued Nov. 14,1978, which is provided as Theoretical Example 1. A solution of 396.07grams of KOH in 10,000 grams of water is introduced into a verticaltubular reactor of 2,000 mm length and 50 mm internal diameter which ispacked with V2A steel Raschig rings of 6 mm diameter. The solution isheated to 45° C. and is mixed by means of a centrifugal pump, with amixing effect corresponding to 1,950 revolutions per minute. 120 gramsof oxygen are introduced from the reactor top and the pressure is set to20.5 bars. In the course of 5 minutes 1,000 grams of an aqueous solutioncontaining 396.32 grams of D-glucose, monohydrate are added, using ametering pump, at the reactor top, to the alkaline solution, which iscirculated by means of the centrifugal pump (1,950 revolutions perminute) in a downward direction via the reactor top. The solution is nowmixed for 9 hours at 1,950 revolutions per minute and kept at 45° C. and20.5 bars. It is then concentrated under 15 mbars until 500 grams ofresidue are left. This material is introduced into 6,000 grams ofmethanol, while stirring, whereupon crystalline potassium arabonateprecipitates. Filtration gives a theoretical yield of 408.44 grams ofpotassium arabonate of melting point 203-204° C. (with decomposition).

TABLE 3 ¹³C-NMR spectrum data [internal standard: sodium salt of 3-(trimethylsilyl)-propanesulphonic acid] ¹³C-NMR chemical Carbon atomshift (ppm) 1 181.9 2 75.0 3 74.4 4 74.1 5 65.9

Theoretical Examples 2-5 Oxidative Decarboxylation and Hydrogenation ofGlucose to Arabinitol

Other suitable examples of reactions for the oxidative decarboxylationof a glucose starting material to arabinonate, and the conversion ofarabinonate to arabinitol, are provided in U.S. Pat. No. 5,831,078 toElseviers et al., filed Jul. 23, 1997 and issued Nov. 3, 1998, which areprovided as Theoretical Examples 2-5 below.

Theoretical Example 2 Oxidative Decarboxylation Applying Oxygen Gas at 2Bar Pressure

A glucose solution (1.5 kg-10% w/w solution) starting material is heatedto 45° C. in a two liter autoclave while stirring at 1000 rpm. Thereactor containing the glucose solution is purged twice for 0.5 minuteswith oxygen gas at 1 bar pressure. After purging, the oxygen pressure inthe reactor is adjusted to 2 bar. The reaction is started by dosing thepotassium hydroxide solution (242 g-50% w/w solution) with a dosingburette to the glucose solution using a dosing speed of 1.3 mol KOH/h.The total dosing time required is 1.7 hours. The reaction mixture isstirred for a total reaction time of 5 hours, including the dosing timeof the alkali. The product is determined by HPLC analysis (see Table 4).

TABLE 4 Theoretical O₂ Example atmospheric O₂ at 2 bar No. H₂O₂ used?pressure pressure 2 No 55% 88% 3 Yes N/A 83%

Theoretical Example 3 Oxidative Decarboxylation With Oxygen Pressure of2 Bar and Addition of Hydrogen Peroxide

The experiment of theoretical example 2 may be performed using glucosesolutions at 10%, 20% and 30% dry substance, applying 2 bar oxygenpressure at 40° C.

The glucose solution is heated to 40° C. in a two liter autoclave whilestirring at 1000 ppm. The reactor containing the glucose solution ispurged twice for 0.5 minutes with oxygen gas at 1 bar pressure. Afterpurging, the oxygen pressure in the reactor is adjusted to 2 bar. Thereaction is started by dosing the sodium hydroxide solution (45% w/wsolution) with a dosing burette to the glucose solution using a dosingspeed of 0.65 mol NaOH/h.

TABLE 5 Glucose starting material conc'n Molar yield arabinonate 10% 89%20% 87% 30% 80%

Theoretical Example 4 Purification of Arabinonate, Followed byProtonation and Hydrogenation to Arabinitol Crystallization

Before crystallizing the alkali metal arabinonate (being sodiumarabinonate or potassium arabinonate), the crude reaction mixture isbrought to pH=7 with the aid of ion exchange resin (e.g. Lewatit S2528).

The resulting reacting mixture (pH=7) is concentrated under reducedpressure at 50° C. to 70% dry substance. The crystals are collected byfiltration or centrifugation and are dried at room temperature. Sodiumarabinonate is obtained in 95-97% purity and potassium arabinonate isobtained in 98-99% purity. The remaining impurities are glycolate andformate.

Recrystallization

The collected crystals are dissolved again in water to obtain a 70%solution. Cooling down to room temperature allows the crystallization ofsodium arabinonate, obtained in 100% purity. This recrystallization ismost of the time required to remove all traces of formate. Completeremoval is preferred because any trace of formic acid may poison thecatalyst.

Theoretical Example 5 Protonation With Ion Exchange Resin

The protonation of alkali metal arabinonate to arabinonic acid ispreferably performed with ion exchange resin (e.g. Mitsubishi UBK 550,Lewatit S2528). This arabinonic acid is then used as a starting materialfor the electrolytic decarboxylation.

The described embodiments and examples are to be considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is, therefore, indicated by the appended claims rather than bythe foregoing description. All changes which come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

1. A method of producing erythrose, comprising the steps of: providingan acid solution comprising an acid selected from the group consistingof a ribonic acid and an arabinonic acid, the acid solution havingbetween about 10% and 100% of the acid neutralized; and electrolyticallydecarboxylating the acid in the acid solution to produce erythrose. 2.The method of claim 1, where the acid is D- or L-arabinonic acid or asalt thereof.
 3. The method of claim 1, where the ribonic acid orarabinonic acid solution is between about 35% and about 80% neutralizedprior to the electrolytic decarboxylation step.
 4. The method of claim1, where the electrolytic decarboxylation is performed at least untilabout 80% of the acid is converted to erythrose.
 5. The method of claim1, wherein the acid solution comprises the acid and a solvent selectedfrom the group consisting of: water and a water-miscible solvent.
 6. Themethod of claim 5, wherein the water-miscible solvent is selected fromthe group consisting of: water, methanol, ethanol, propanol, dioxane andacetonitrile.
 7. The method of claim 1, wherein the electrolyticdecarboxylation of the acid solution is performed by contacting the acidsolution with an anode.
 8. The method of claim 7, wherein theelectrolytic decarboxylation of the acid solution is performed bycontacting the acid solution with an anode that is a highly graphiticelectrode.
 9. The method of claim 7, wherein the electrolyticdecarboxylation of the acid solution is performed by contacting the acidsolution with an anode that is a graphite foil electrode.
 10. The methodof claim 7, wherein the electrolytic decarboxylation of the acidsolution is performed by contacting the acid solution with a portion ofan electrolytic cell having a divided, undivided, flow-through, packedbed, batch cell or fluidized bed configuration.
 11. The method of claim4, further comprising the step of recycling of residual arabinonic acidor a salt thereof.
 12. A method of producing erythrose, comprising thesteps of: decarboxylating a sugar selected from the group consisting of:allose, altrose, glucose, fructose and mannose, to produce an acidselected from the group consisting of: ribonic acid and arabinonic acid;combining the acid with a solvent to produce an acid solution comprisingone or more acids selected from the group consisting of a ribonic acidand an arabinonic acid, the acid solution having between about 10% and100% of at least one acid neutralized; and electrolyticallydecarboxylating the acid in the acid solution to produce erythrose. 13.The method of claim 12, wherein the solvent comprises water or awater-miscible solvent, the acid is arabinonic acid and the sugarcomprises glucose, fructose or mannose.
 14. The method of claim 13,wherein the sugar comprises glucose or fructose, and wherein betweenabout 40% and 60% of the acid solution is neutralized prior to theelectrolytic decarboxylation.
 15. The method of claim 14, wherein theelectrolytic decarboxylation of the acid solution is performed bycontacting the acid solution with a highly graphitic electrodeconfigured as an anode.
 16. A method of producing erythritol, comprisingthe steps of: providing an acid solution comprising an acid selectedfrom the group consisting of a ribonic acid and an arabinonic acid, theacid solution having between about 10% and 100% of the acid neutralized;electrolytically decarboxylating the acid in the acid solution toproduce erythrose; and hydrogenating the erythrose to convert theerythrose to erythritol.
 17. The method of claim 16, wherein thehydrogenation of erythrose is performed in the presence of a catalystcomprising nickel or ruthenium.
 18. The method of claim 16, furthercomprising the step of adjusting the pH of the acid solution to providean acid solution having about 40% to 60% of the acid neutralized priorto performing the electrolytic decarboxylation of the acid in the acidsolution.
 19. The method of claim 16, wherein the erythrose is convertedto erythritol by electrolytic reduction at a cathode.
 20. The method ofclaim 16, wherein the method comprises the steps of: providing anaqueous arabonate solution; acidifying the arabonate solution bycontacting the arabonate solution with a cation exchange resin at asuitable pH to provide about 40-60% neutralization of the arabonatesolution to form an arabinonic acid solution; isolating the arabinonicacid solution from the cation exchange resin; electrolyticallydecarboxylating the arabinonic acid in the arabinonic acid solution bycontacting the arabinonic acid solution with an anode comprising ahighly crystalline graphite foil electrode to produce erythrose; andconverting the erythrose to erythritol by adding a hydride reducingagent to a solution comprising the erythrose.